The present invention relates to a hydraulic control unit of an electronically controlled hydraulic brake system capable of performing functions like anti-lock control, traction control or electronic stability control. Such brake systems include a plurality of valves for modulating the hydraulic brake pressure in the wheel brakes. Brake fluid relieved from the wheel brakes during an anti-lock braking operation is collected in at least one low-pressure accumulator, from where it is returned into the brake line by means of at least one hydraulic pump.
Usually, each one of two brake circuits includes one low-pressure accumulator and one pump, wherein the two pumps of the two separate brake circuits are jointly driven by one electric motor. The motor drives a rotating cam arranged between two radial pump pistons, one for each brake circuit. The pump pistons are pushed outward by the rotating cam in an alternating order and are returned either by spring force or by fluid pressure prevailing on the other side of the respective piston.
The hydraulic control unit generally comprises a machined housing accommodating the cam shaft and the pump pistons, wherein the cam shaft extends to the outside of the housing where the motor is attached. The housing also includes recesses for the low-pressure accumulators. Each low-pressure accumulator has an accumulator chamber separated from a spring chamber by means of an accumulator piston which is biased toward the accumulator chamber by a compression spring. The accumulator chamber is located toward the interior the housing so that the spring, which abuts an accumulator cap closing of the low-pressure accumulator of toward the atmosphere, urges the accumulator piston toward the interior of the housing.
Due to the movement of the pistons, a pump may experience minor leakage of brake fluid. This leaked brake fluid can usually seep past the pistons back into the brake system once the brake operation is finished and the fluid pressure on the pressure side of the pistons becomes equal to atmospheric pressure.
However, if a vehicle is designed to be an amphibian or submersible vehicle, the brake system is surrounded by water. This penetrating water can then flush the leaked brake fluid into the housing of the electric motor. Brake fluid is highly corrosive an may damage the electric motor.
It is therefore the objective of the present invention to provide a hydraulic control unit which is suited for a submersible vehicle.
Another objective of the present invention is to provide a low-cost solution for the problem.